Ok, so I really don't know where to look for information to rebutt this. I mean I know what I want to say, but I want to reply with info that will sink into this person. So here is what he has given me:
As for your rain argument, here's a little thought for you. It's a bit complicated and requires an understanding of Biblical law.
The Bible in Leviticus 25 talks about the "remission year" or "fallow year" that the Israelites must observe every 7th year inside the Land of Israel. (This is called "shmitah" in Hebrew.) The law requires that Jews (including modern Jews living in Israel) not work their land every 7th year... they cannot plant, sow, reap, or otherwise work the land. They cannot obtain food from the land. Which means that they must have enough food reserves from the prior year to last through the 7th year.
That means that every 7 years on the 6th year of the cycle, the land must produce TWICE AS MUCH as usual in order for the people to survive... especially in ancient times when their were living in a subsistance agrarian economy.
Part of God's promise to the Jews was that if they follow these laws, he would make sure they had enough to eat, even though they didn't work the land.
The Bible in Leviticus 25 also requires that Jews observe the Jubillee year every 50th year. ("Yovel" in Hebrew.) One of the requirements of the Jubillee year is that the land remain fallow, just as in the Shmitah year.
Let's do some math for a moment... according to my calculations, the Shmitah year would be in year 7, year 14, year 21... and year 49. The Jubillee year would take place in year 50.
That means that there are two fallow years in a row... years 49 and 50. And that means that, in this ancient subsistance agrarian economy, the land in year 48 had to produce THREE TIMES AS MUCH FOOD AS USUAL... enough for years 48, 49 AND 50. And it had to do so BEFORE lying fallow... at a time when the land has already been used to its fullest potential for the prior 6 years and needs a "rest".
Yet, God's blessing that the land would provide enough for all the people even durring the fallow years has managed to hold true for literally THOUSANDS of years. Throughout that entire time there have been Jews following these fallow laws, and never once has the land failed to produce as promised due to drought, famine, disease... the land has produced in accordance with God's promise every time.
It seems to me that prayer/worship definitely DOES result in good weather as needed. You can't produce twice or three times as much food as normal in bad weather.
How do I know that it never failed? Because if it had failed, the Jewish people would have known that God's promise was fake and would have stopped following the laws. Yet they kept the laws, and still do, because God demonstrates time and again that his promise is the real deal by making sure the land produces as much as is necessary to keep the people alive. The evidence is in the people and their actions.
What this tells me is that prayer/worship does have a real, tangible effect... if you are willing to recognize it as such.